1. Technical Field
The present invention generally relates to optical proximity correction (OPC) and, particularly to a method to compensate optical proximity correction for shallow trench isolation (STI) effect.
2. Description of the Related Art
An integrated circuit (IC) layout generally includes active regions, a shallow trench isolation (STI) region and ion implant regions overlapped with a part of the STI region and a part of the active regions. The STI region is a region except the active regions. Before an ion implanting process is performed to the implant regions, a photolithography process firstly is carried out to form a photoresist pattern on a substrate and whereby the ion implant regions are exposed. However, since different patterns on the substrate would cause light to be influenced resulting from different light reflectivity during exposure, which would result in the photoresist pattern occurring critical dimension variation after developing, i.e., the actual critical dimension of the developed photoresist pattern does not meet target. In order to obtain a proper photoresist pattern after exposure, it is necessary to perform optical proximity correction for photomask.
In particular, before the photoresist pattern is formed, an anti-reflective coating layer is firstly formed on the substrate to avoid the critical dimension variation of the developed photoresist pattern caused by light reflection during exposure. However, since the ion implant regions are needed to be ion implanted in subsequent process, the anti-reflective coating layer could not cover the ion implant regions. Therefore, the incident light would readily be reflected by silicon and oxide films in the ion implant regions during exposure, together with the shallow trench isolation topography influence, which result in the traditional optical proximity correction would not accurately correct the photomask, and the critical dimension variation occurred as a result. The issue of critical dimension variation may cause the edges of the ion implant regions are covered by photoresist or cause photoresist peeling. Herein, the photoresist peeling is a phenomenon of the photoresist being cracked resulting from excessive small line width thereof.